In hitherto known control systems for internal combustion engines provided with electronic fuel injection control apparatus, deceleration of the engine is detected on the basis of the position or opening degree of a throttle valve and the revolution speed of the engine crankshaft. When deceleration of the engine is determined from the fact that the throttle valve is at the fully closed position while the engine is operated at a higher speed than a predetermined value, the fuel injection is stopped or interrupted, thereby enhancing the action of engine braking and at the same time reducing fuel consumption. However, when the normal fuel injection is restored with normal ignition timing after interruption, the rotational moment or torque of the engine will be increased abruptly, involving shocks or the like adverse influences to the comfortable ride in an associated motor vehicle. Such undersirable phenomena are particularly noticeable when the engine speed is very low immediately before the fuel injection is re-initiated. Accordingly, in order to avoid such a discomfort, the revolution speed of the engine crankshaft at which fuel injection is to be re-initiated after interruption has to be set at a relatively high value which, however, means that the action of engine braking as well as the advantage with respect to fuel consumption must be correspondingly sacrificed.
As attempts to overcome the difficulty described above, improvements of the fuel injection system have heretofore been proposed. For example, in Japanese Patent Application Laid-open No. 64633/75 and Japanese Utility Model Application Laid-open No. 41524/78, it is proposed that the quantity of fuel to be injected is progressively increased to a normal quantity upon restoration of the fuel injection after the interruption thereof to thereby assure a comfortable ride.